From da9803bc8812f5bd3b26baaa90e515b843c65ff7 Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 21 Aug 2013 17:29:38 -0400 Subject: FS-Cache: Add interface to check consistency of a cached object Extend the fscache netfs API so that the netfs can ask as to whether a cache object is up to date with respect to its corresponding netfs object: int fscache_check_consistency(struct fscache_cookie *cookie) This will call back to the netfs to check whether the auxiliary data associated with a cookie is correct. It returns 0 if it is and -ESTALE if it isn't; it may also return -ENOMEM and -ERESTARTSYS. The backends now have to implement a mandatory operation pointer: int (*check_consistency)(struct fscache_object *object) that corresponds to the above API call. FS-Cache takes care of pinning the object and the cookie in memory and managing this call with respect to the object state. Original-author: Hongyi Jia Signed-off-by: David Howells cc: Hongyi Jia cc: Milosz Tanski --- Documentation/filesystems/caching/backend-api.txt | 9 +++++++++ Documentation/filesystems/caching/netfs-api.txt | 17 +++++++++++++---- 2 files changed, 22 insertions(+), 4 deletions(-) (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/caching/backend-api.txt b/Documentation/filesystems/caching/backend-api.txt index d78bab9622c6..277d1e810670 100644 --- a/Documentation/filesystems/caching/backend-api.txt +++ b/Documentation/filesystems/caching/backend-api.txt @@ -299,6 +299,15 @@ performed on the denizens of the cache. These are held in a structure of type: enough space in the cache to permit this. + (*) Check coherency state of an object [mandatory]: + + int (*check_consistency)(struct fscache_object *object) + + This method is called to have the cache check the saved auxiliary data of + the object against the netfs's idea of the state. 0 should be returned + if they're consistent and -ESTALE otherwise. -ENOMEM and -ERESTARTSYS + may also be returned. + (*) Update object [mandatory]: int (*update_object)(struct fscache_object *object) diff --git a/Documentation/filesystems/caching/netfs-api.txt b/Documentation/filesystems/caching/netfs-api.txt index 97e6c0ecc5ef..12b344251523 100644 --- a/Documentation/filesystems/caching/netfs-api.txt +++ b/Documentation/filesystems/caching/netfs-api.txt @@ -32,7 +32,7 @@ This document contains the following sections: (9) Setting the data file size (10) Page alloc/read/write (11) Page uncaching - (12) Index and data file update + (12) Index and data file consistency (13) Miscellaneous cookie operations (14) Cookie unregistration (15) Index invalidation @@ -690,9 +690,18 @@ written to the cache and for the cache to finish with the page generally. No error is returned. -========================== -INDEX AND DATA FILE UPDATE -========================== +=============================== +INDEX AND DATA FILE CONSISTENCY +=============================== + +To find out whether auxiliary data for an object is up to data within the +cache, the following function can be called: + + int fscache_check_consistency(struct fscache_cookie *cookie) + +This will call back to the netfs to check whether the auxiliary data associated +with a cookie is correct. It returns 0 if it is and -ESTALE if it isn't; it +may also return -ENOMEM and -ERESTARTSYS. To request an update of the index data for an index or other object, the following function should be called: -- cgit v1.2.3 From 696f69b6b088f0f5b9470a5d008871c96354f531 Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 5 Sep 2013 13:06:15 +0100 Subject: FS-Cache: Fix heading in documentation Fix a heading in the documentation to make it consistent with the contents list. Signed-off-by: David Howells --- Documentation/filesystems/caching/netfs-api.txt | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/caching/netfs-api.txt b/Documentation/filesystems/caching/netfs-api.txt index 12b344251523..26c1dd5a6a21 100644 --- a/Documentation/filesystems/caching/netfs-api.txt +++ b/Documentation/filesystems/caching/netfs-api.txt @@ -433,7 +433,7 @@ to the caller. The attribute adjustment excludes read and write operations. ===================== -PAGE READ/ALLOC/WRITE +PAGE ALLOC/READ/WRITE ===================== And the sixth step is to store and retrieve pages in the cache. There are -- cgit v1.2.3 From 5a6f282a2052bb13171b53f03b34501cf72c33f1 Mon Sep 17 00:00:00 2001 From: Milosz Tanski Date: Wed, 21 Aug 2013 17:30:11 -0400 Subject: fscache: Netfs function for cleanup post readpages Currently the fscache code expect the netfs to call fscache_readpages_or_alloc inside the aops readpages callback. It marks all the pages in the list provided by readahead with PG_private_2. In the cases that the netfs fails to read all the pages (which is legal) it ends up returning to the readahead and triggering a BUG. This happens because the page list still contains marked pages. This patch implements a simple fscache_readpages_cancel function that the netfs should call before returning from readpages. It will revoke the pages from the underlying cache backend and unmark them. The problem was originally worked out in the Ceph devel tree, but it also occurs in CIFS. It appears that NFS, AFS and 9P are okay as read_cache_pages() will clean up the unprocessed pages in the case of an error. This can be used to address the following oops: [12410647.597278] BUG: Bad page state in process petabucket pfn:3d504e [12410647.597292] page:ffffea000f541380 count:0 mapcount:0 mapping: (null) index:0x0 [12410647.597298] page flags: 0x200000000001000(private_2) ... [12410647.597334] Call Trace: [12410647.597345] [] dump_stack+0x19/0x1b [12410647.597356] [] bad_page+0xc7/0x120 [12410647.597359] [] free_pages_prepare+0x10e/0x120 [12410647.597361] [] free_hot_cold_page+0x40/0x170 [12410647.597363] [] __put_single_page+0x27/0x30 [12410647.597365] [] put_page+0x25/0x40 [12410647.597376] [] ceph_readpages+0x2e9/0x6e0 [ceph] [12410647.597379] [] __do_page_cache_readahead+0x1af/0x260 [12410647.597382] [] ra_submit+0x21/0x30 [12410647.597384] [] filemap_fault+0x254/0x490 [12410647.597387] [] __do_fault+0x6f/0x4e0 [12410647.597391] [] ? __switch_to+0x16d/0x4a0 [12410647.597395] [] ? finish_task_switch+0x5a/0xc0 [12410647.597398] [] handle_pte_fault+0xf6/0x930 [12410647.597401] [] ? pte_mfn_to_pfn+0x93/0x110 [12410647.597403] [] ? xen_pmd_val+0xe/0x10 [12410647.597405] [] ? __raw_callee_save_xen_pmd_val+0x11/0x1e [12410647.597407] [] handle_mm_fault+0x251/0x370 [12410647.597411] [] ? call_rwsem_down_read_failed+0x14/0x30 [12410647.597414] [] __do_page_fault+0x1aa/0x550 [12410647.597418] [] ? up_write+0x1d/0x20 [12410647.597422] [] ? vm_mmap_pgoff+0xbc/0xe0 [12410647.597425] [] ? SyS_mmap_pgoff+0xd8/0x240 [12410647.597427] [] do_page_fault+0xe/0x10 [12410647.597431] [] page_fault+0x28/0x30 Signed-off-by: Milosz Tanski Signed-off-by: David Howells --- Documentation/filesystems/caching/netfs-api.txt | 18 +++++++++++++++++- fs/fscache/page.c | 16 ++++++++++++++++ include/linux/fscache.h | 22 ++++++++++++++++++++++ 3 files changed, 55 insertions(+), 1 deletion(-) (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/caching/netfs-api.txt b/Documentation/filesystems/caching/netfs-api.txt index 26c1dd5a6a21..11a0a40ce445 100644 --- a/Documentation/filesystems/caching/netfs-api.txt +++ b/Documentation/filesystems/caching/netfs-api.txt @@ -499,7 +499,7 @@ Else if there's a copy of the page resident in the cache: (*) An argument that's 0 on success or negative for an error code. If an error occurs, it should be assumed that the page contains no usable - data. + data. fscache_readpages_cancel() may need to be called. end_io_func() will be called in process context if the read is results in an error, but it might be called in interrupt context if the read is @@ -623,6 +623,22 @@ some of the pages being read and some being allocated. Those pages will have been marked appropriately and will need uncaching. +CANCELLATION OF UNREAD PAGES +---------------------------- + +If one or more pages are passed to fscache_read_or_alloc_pages() but not then +read from the cache and also not read from the underlying filesystem then +those pages will need to have any marks and reservations removed. This can be +done by calling: + + void fscache_readpages_cancel(struct fscache_cookie *cookie, + struct list_head *pages); + +prior to returning to the caller. The cookie argument should be as passed to +fscache_read_or_alloc_pages(). Every page in the pages list will be examined +and any that have PG_fscache set will be uncached. + + ============== PAGE UNCACHING ============== diff --git a/fs/fscache/page.c b/fs/fscache/page.c index 793e3d5ca4b5..8702b732109a 100644 --- a/fs/fscache/page.c +++ b/fs/fscache/page.c @@ -700,6 +700,22 @@ nobufs: } EXPORT_SYMBOL(__fscache_alloc_page); +/* + * Unmark pages allocate in the readahead code path (via: + * fscache_readpages_or_alloc) after delegating to the base filesystem + */ +void __fscache_readpages_cancel(struct fscache_cookie *cookie, + struct list_head *pages) +{ + struct page *page; + + list_for_each_entry(page, pages, lru) { + if (PageFsCache(page)) + __fscache_uncache_page(cookie, page); + } +} +EXPORT_SYMBOL(__fscache_readpages_cancel); + /* * release a write op reference */ diff --git a/include/linux/fscache.h b/include/linux/fscache.h index d984aff32a11..19b46458e4e8 100644 --- a/include/linux/fscache.h +++ b/include/linux/fscache.h @@ -209,6 +209,8 @@ extern bool __fscache_maybe_release_page(struct fscache_cookie *, struct page *, gfp_t); extern void __fscache_uncache_all_inode_pages(struct fscache_cookie *, struct inode *); +extern void __fscache_readpages_cancel(struct fscache_cookie *cookie, + struct list_head *pages); /** * fscache_register_netfs - Register a filesystem as desiring caching services @@ -589,6 +591,26 @@ int fscache_alloc_page(struct fscache_cookie *cookie, return -ENOBUFS; } +/** + * fscache_readpages_cancel - Cancel read/alloc on pages + * @cookie: The cookie representing the inode's cache object. + * @pages: The netfs pages that we canceled write on in readpages() + * + * Uncache/unreserve the pages reserved earlier in readpages() via + * fscache_readpages_or_alloc() and similar. In most successful caches in + * readpages() this doesn't do anything. In cases when the underlying netfs's + * readahead failed we need to clean up the pagelist (unmark and uncache). + * + * This function may sleep as it may have to clean up disk state. + */ +static inline +void fscache_readpages_cancel(struct fscache_cookie *cookie, + struct list_head *pages) +{ + if (fscache_cookie_valid(cookie)) + __fscache_readpages_cancel(cookie, pages); +} + /** * fscache_write_page - Request storage of a page in the cache * @cookie: The cookie representing the cache object -- cgit v1.2.3